Testing of electrical circuits is frequently required in situations where it is not always practical to use a large professional circuit testing device. For example, testing of the ignition circuits in automobiles, and small engines such as lawn mowers, boats and the like is often carried out without any instruments at all, simply by checking various plug leads. This operation requires two people, one to crank the engine and the other to watch for the occurrence of a spark. In addition, this method of testing is crude and unreliable, and often results in shock hazards.
Testing of ignition components, such as the capacitor, is impossible using these techniques.
For these reasons, it is apparent that there is a need for a low cost light-weight portable circuit testing device which can be used for checking a variety of different types of circuits, for example engine high tension circuits, and low voltage circuits, and is of such a design that it can be manufactured and sold at a relatively low cost and is reliable in use and is as far as possible safe from electrical shock hazards to the user, or damage by misuse.